docs: def for_json(self):
          """Return date ISO8601 string formats for datetime, date, and time values, milliseconds for intervals"""
          value = super(DatetimeField, self).for_json()
  
          # Order of instance checks matters for proper inheritance checks
          if isinstance(value, pendulum.Interval):
              return value.in_seconds() * 1000
          if isinstance(value, datetime):
              return self.format_datetime(value)
          if isinstance(value, pendulum.Time):
              return str(value)
          if isinstance(value, pendulum.Date):
              return value.to_date_string()